The present invention relates to an abnormality diagnosis apparatus for an evaporative fuel processing system which stores evaporative fuel, generated in a fuel tank, in a canister and purges the evaporative fuel stored in the canister into an intake system of an internal combustion engine at appropriate timings.
As disclosed in Japanese Patent laid-Open No. Hei 9-126064, the abnormality diagnosis for an evaporative fuel processing system for a vehicle is executed under a condition wherein the vehicle is in a so-called cruising state. In other words, the operation of the engine is in the stationary state. The abnormality diagnosis is executed by introducing a negative pressure from an intake system of the engine into the evaporative fuel processing system. Accordingly, at the time the negative pressure is introduced, that is, during the process of reducing the pressure in the evaporative fuel processing system, the amount of the evaporative fuel purged into the intake system tends to increase. Therefore, in order to reduce the purging of the evaporative fuel during the pressure reduction processing abnormality diagnosis is executed under the above-described condition when the vehicle is in the cruising state where the engine is in a stationary condition.
However, depending on the manner in which the user operates the vehicle, there is a possibility that a vehicle operating state capable of executing the abnormality diagnosis, (i.e., a vehicle operating state satisfying the abnormality diagnosis execution condition) may not be obtained. Accordingly, it is also necessary to execute the abnormality diagnosis even in an idling condition of the engine. However, if the above-described conventional abnormality diagnosis executed in the cruising state of the vehicle is applied to the abnormality diagnosis in the idling condition of the engine, the amount of evaporative fuel purged into an intake system of the engine may become excessively large. The large amount of evaporated fuel purged into the intake system may cause the engine to stall since the conventional abnormality diagnosis can only be executed under the condition when the vehicle is in the cruising state.
An object of the present invention is to provide an abnormality diagnosis apparatus for an evaporative fuel processing system, which is capable of executing an abnormality diagnosis which includes a process of reducing a pressure in the evaporative fuel processing system without causing the engine to stall, especially when the engine is in an idling condition.
In order to achieve the above object, the present invention provides an abnormality diagnosis apparatus for performing a leak check and determining whether or not a leak exists in an evaporative fuel processing system, including a fuel tank, a canister for storing evaporative fuel generated in the fuel tank, a charging passage for connecting the fuel tank to the canister, a purging passage for connecting the canister to an intake system of an internal combustion engine, and a purge control valve provided in the purging passage. Additionally, the abnormality diagnosis apparatus comprises: a pressure sensor for detecting a pressure in the evaporative fuel processing system; pressure reduction processing means for executing a process of reducing the pressure in the evaporative fuel processing system with a limited flow rate of gases passing through the purge control valve when performing the leak check in an idling condition of the engine, the limited flow rate being set to a value equal to or smaller than a predetermined flow rate which is smaller than the maximum flow rate applied to the leak check performed in operating conditions of the engine other than the idling condition; and leak determining means for performing the leak check on the basis of a change in the pressure in the evaporative fuel processing system after the pressure reduction process.
According to the present invention, the process of reducing the pressure in the evaporative fuel processing system is executed with a limited flow rate of gases passing through the purge control valve when performing the leak check of the evaporative fuel processing system in the idling condition of the engine. Specifically, the flow rate is limited to a value equal to or smaller than a predetermined flow rate which is smaller than the maximum flow rate applied to the leak check performed in operating conditions other than the idling condition. After the pressure reduction process, the leak check is performed on the basis of a change in the pressure in the evaporative fuel processing system. Accordingly, the abnormality diagnosis for the evaporative fuel processing system can be performed without rapidly increasing an amount of the evaporative fuel supplied to the intake system of the engine even if the engine is in the idling condition and thereby preventing the inconvenience such as engine stall.
Preferably, the abnormality diagnosis apparatus is an external apparatus provided separately from the engine and a control system. The control system is connected to the evaporative fuel processing system and controls the evaporative fuel processing system. The abnormality diagnosis apparatus performs the leak check by supplying an execution command signal to the control system.
According to the present invention, the abnormality diagnosis can be arbitrarily executed by connecting the abnormality diagnosis apparatus, an external apparatus provided separately from the engine, to the control system in the idling condition of the engine. Therefore, the abnormality diagnosis for the evaporative fuel processing system can be easily executed at the time of inspection or maintenance of the vehicle.
Preferably, the pressure sensor is mounted in the charging passage; and the pressure reduction processing means executes the pressure reduction process by comparing a pressure detected by the pressure sensor with each of a first predetermined pressure (POBJH) and a second predetermined pressure (POBJL) lower than the first predetermined pressure, and gradually increasing the valve opening amount of the purge control valve when the detected pressure reaches the first predetermined pressure while gradually decreasing the valve opening amount of the purge control valve when the detected pressure reaches the second predetermined pressure.
Preferably, the second predetermined pressure is set so that the second predetermined pressure gradually becomes closer to the first predetermined pressure with elapsed time.
Preferably, the leak determining means corrects a raised amount (xcex94P2) of pressure in the evaporative fuel processing system within a predetermined time period, after the pressure reduction process, by the pressure reduction processing means, according to a pressure change (xcex94P1) which depends on the amount of evaporative fuel generated in the fuel tank. Furthermore, the leak determining means determines that there exists a leak in the evaporative fuel processing system, when a pressure raised amount (xcex94P2xe2x88x92xcex94P1), after correction, is larger than a predetermined pressure change amount (xcex94PLEAK).
Preferably, the abnormality diagnosis apparatus according to the present invention further includes a first evaporative fuel amount determining means for determining an amount of the evaporative fuel generated in the fuel tank during the pressure reduction processing, wherein the pressure reduction process is interrupted when it is determined by the first evaporative fuel amount determining means that the evaporative fuel amount is larger than a first predetermined amount.
Preferably, the abnormality diagnosis apparatus according to the present invention further includes an oxygen concentration sensor for detecting an oxygen concentration in the exhaust gases from the engine, wherein the first evaporative fuel amount determining means determines the evaporative fuel amount on the basis of an air-fuel ratio correction coefficient (KO2) set according to an output of the oxygen concentration sensor.
Preferably, the abnormality diagnosis apparatus according to the present invention further includes a second evaporative fuel amount determining means for determining an amount of the evaporative fuel generated in the fuel tank after measurement of the pressure raised amount (xcex94P2), wherein the determination of whether or not a leak exists in the evaporative fuel processing system is withheld when it is determined by the second evaporative fuel amount determining means that the evaporative fuel amount is larger than a second predetermined amount.
The above and other objectives, features and advantages of the present invention will becomes apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements are denoted by like reference symbols.